Combiner.java

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package net.sourceforge.plantuml.project.ngm.math;

import java.time.LocalDateTime;
import java.util.Arrays;
import java.util.List;
import java.util.function.BiFunction;
import java.util.stream.Collectors;

/**
 * Utilities to combine multiple {@link PiecewiseConstant} functions.
 *
 * <p>
 * In the New Gantt Model context, {@link PiecewiseConstant} typically
 * represents a time-dependent workload allocation expressed as a
 * {@link Fraction}.
 * </p>
 *
 * <p>
 * This class is also a {@link PiecewiseConstant}: it can represent the
 * combination of several piecewise-constant functions using a combiner
 * operation (sum, product, min, max...).
 * </p>
 */
public class Combiner extends AbstractPiecewiseConstant {

	private final List<PiecewiseConstant> elements;

	private final BiFunction<Fraction, Fraction, Fraction> operation;

	private Combiner(BiFunction<Fraction, Fraction, Fraction> operation, PiecewiseConstant... elements) {
		this.elements = Arrays.asList(elements);
		this.operation = operation;
	}

	public static PiecewiseConstant sum(PiecewiseConstant... elements) {
		if (elements.length == 1)
			return elements[0];
		return new Combiner(Fraction.SUM, elements);
	}

	public static PiecewiseConstant min(PiecewiseConstant... elements) {
		if (elements.length == 1)
			return elements[0];
		return new Combiner(Fraction.MIN, elements);
	}

	public static PiecewiseConstant max(PiecewiseConstant... elements) {
		if (elements.length == 1)
			return elements[0];
		return new Combiner(Fraction.MAX, elements);
	}

	public static PiecewiseConstant product(PiecewiseConstant... elements) {
		if (elements.length == 1)
			return elements[0];
		return new Combiner(Fraction.PRODUCT, elements);
	}

	@Override
	public Segment segmentAt(LocalDateTime instant, TimeDirection direction) {
		if (elements.size() < 2)
			throw new IllegalStateException("At least two functions are required for combination");

		final List<Segment> segments = elements.stream().map(f -> f.segmentAt(instant, direction))
				.collect(Collectors.toList());

		return Segment.intersection(segments, operation);
	}

}